Handling concurrency violations

**=?Utf-8?B?S2VycnkgTW9vcm1hbg==?=** · Mar 26 '08, 11:45 AM

RE: Handling concurrency violations

John,

It looks like your approach to concurrency handling is to get around the
concurrency error by reloading the data from the database and then applying
your changes.

You might as well just turn off concurrency checking, since that is the end
result anyway.

In other words, it looks like your code is just avoiding concurrency
exceptions, not handling concurrency conflicts.

Kerry Moorman

"John" wrote:

Hi
>
I have developed the following logic to handle db concurrency violations. I
just wonder if someone can tell me if it is correct or if I need a
different approach.Would love to know how pros handle it.
>
Thanks
>
Regards
>
>
Dim dc As DataColumn
Dim drCache As DataRow
Dim drCurrent As DataRow
>
Try
' Attempt the update
daContacts.Upda te(ds.Contacts)
>
Catch Ex As DBConcurrencyEx ception
>
' First - cache the row
drCache = ds.Contacts.New Row()
For Each dc In ds.Contacts.Col umns
If Not dc.ReadOnly Then
drCache(dc.Colu mnName) = Ex.Row(dc.Colum nName)
End If
Next
>
' Refresh from database
daContacts.Fill (ds.Contacts)
>
' Position to the faulted row
drCurrent = ds.Contacts.Row s.Find(Ex.Row(" ID"))
>
' Apply User Changes
For Each dc In ds.Contacts.Col umns
If Not dc.ReadOnly Then
drCurrent(dc.Co lumnName) = drCache(dc.Colu mnName)
End If
Next
>
' Save again
daContacts.Upda te(ds.Contacts)
End Try
>
>
>

**John** · Mar 26 '08, 06:35 PM

Re: Handling concurrency violations

So Kerry how do I handle it? which was my original question.

Regards

"Kerry Moorman" <KerryMoorman@d iscussions.micr osoft.comwrote in message
news:31F1C265-0B1C-40DB-8174-3A5F6DA4DD8F@mi crosoft.com...

John,
>
It looks like your approach to concurrency handling is to get around the
concurrency error by reloading the data from the database and then
applying
your changes.
>
You might as well just turn off concurrency checking, since that is the
end
result anyway.
>
In other words, it looks like your code is just avoiding concurrency
exceptions, not handling concurrency conflicts.
>
Kerry Moorman
>
"John" wrote:
>

>Hi
>>
>I have developed the following logic to handle db concurrency violations.
>I
>just wonder if someone can tell me if it is correct or if I need a
>different approach.Would love to know how pros handle it.
>>
>Thanks
>>
>Regards
>>
>>
> Dim dc As DataColumn
> Dim drCache As DataRow
> Dim drCurrent As DataRow
>>
> Try
> ' Attempt the update
> daContacts.Upda te(ds.Contacts)
>>
> Catch Ex As DBConcurrencyEx ception
>>
> ' First - cache the row
> drCache = ds.Contacts.New Row()
> For Each dc In ds.Contacts.Col umns
> If Not dc.ReadOnly Then
> drCache(dc.Colu mnName) = Ex.Row(dc.Colum nName)
> End If
> Next
>>
> ' Refresh from database
> daContacts.Fill (ds.Contacts)
>>
> ' Position to the faulted row
> drCurrent = ds.Contacts.Row s.Find(Ex.Row(" ID"))
>>
> ' Apply User Changes
> For Each dc In ds.Contacts.Col umns
> If Not dc.ReadOnly Then
> drCurrent(dc.Co lumnName) = drCache(dc.Colu mnName)
> End If
> Next
>>
> ' Save again
> daContacts.Upda te(ds.Contacts)
> End Try
>>
>>
>>

**=?Utf-8?B?S2VycnkgTW9vcm1hbg==?=** · Mar 26 '08, 08:05 PM

Re: Handling concurrency violations

John,

You need to decide how you want to handle concurrency issues in a particular
application.

For example, how do you want to handle this situation:

Mary loads your employee record from the Employees table into the Employee
Manager application. She loaded your record because your cell phone number
has changed and she is updating that piece of information in your record.

While Mary is working on your record, Jim loads your employee record from
the Employees table into the Employee Manager application. He loaded your
record because you have just gotten a big raise and he is updating that piece
of information in your record. He changes your salary and updates your record
in the database.

Mary has now finished changing your cell phone number and attempts to update
your record in the database.

Do you want Mary's update to succeed? If it does you have just lost your
raise because her update will overwrite your new salary that Jim entered with
your old salary as it was when Mary loaded your record.

Do you want Mary's update to fail because of a concurrency conflict? When it
fails, how do you want to deal with the conflict?

Your current code appears to read the updated record and then apply the old
values to it. This gets rid of the concurrency conflict but you still end up
with your old salary instead of your raise.

My choice would be to inform the user that the record has been changed by
another user and let the user reload the record and start over.

Kerry Moorman

"John" wrote:

So Kerry how do I handle it? which was my original question.
>
Regards
>
>
"Kerry Moorman" <KerryMoorman@d iscussions.micr osoft.comwrote in message
news:31F1C265-0B1C-40DB-8174-3A5F6DA4DD8F@mi crosoft.com...

John,

It looks like your approach to concurrency handling is to get around the
concurrency error by reloading the data from the database and then
applying
your changes.

You might as well just turn off concurrency checking, since that is the
end
result anyway.

In other words, it looks like your code is just avoiding concurrency
exceptions, not handling concurrency conflicts.

Kerry Moorman

"John" wrote:

Hi
>
I have developed the following logic to handle db concurrency violations.
I
just wonder if someone can tell me if it is correct or if I need a
different approach.Would love to know how pros handle it.
>
Thanks
>
Regards
>
>
Dim dc As DataColumn
Dim drCache As DataRow
Dim drCurrent As DataRow
>
Try
' Attempt the update
daContacts.Upda te(ds.Contacts)
>
Catch Ex As DBConcurrencyEx ception
>
' First - cache the row
drCache = ds.Contacts.New Row()
For Each dc In ds.Contacts.Col umns
If Not dc.ReadOnly Then
drCache(dc.Colu mnName) = Ex.Row(dc.Colum nName)
End If
Next
>
' Refresh from database
daContacts.Fill (ds.Contacts)
>
' Position to the faulted row
drCurrent = ds.Contacts.Row s.Find(Ex.Row(" ID"))
>
' Apply User Changes
For Each dc In ds.Contacts.Col umns
If Not dc.ReadOnly Then
drCurrent(dc.Co lumnName) = drCache(dc.Colu mnName)
End If
Next
>
' Save again
daContacts.Upda te(ds.Contacts)
End Try
>
>
>

>
>
>

**John** · Mar 26 '08, 08:55 PM

Re: Handling concurrency violations

Hi Kerry

Many thanks for this insight. Is there an easy way to display both new and
old row values to the user to let him/her select?

Thanks

Regards

"Kerry Moorman" <KerryMoorman@d iscussions.micr osoft.comwrote in message
news:287D48C5-72D5-4A42-A59F-211AF9599F66@mi crosoft.com...

John,
>
You need to decide how you want to handle concurrency issues in a
particular
application.
>
For example, how do you want to handle this situation:
>
Mary loads your employee record from the Employees table into the Employee
Manager application. She loaded your record because your cell phone number
has changed and she is updating that piece of information in your record.
>
While Mary is working on your record, Jim loads your employee record from
the Employees table into the Employee Manager application. He loaded your
record because you have just gotten a big raise and he is updating that
piece
of information in your record. He changes your salary and updates your
record
in the database.
>
Mary has now finished changing your cell phone number and attempts to
update
your record in the database.
>
Do you want Mary's update to succeed? If it does you have just lost your
raise because her update will overwrite your new salary that Jim entered
with
your old salary as it was when Mary loaded your record.
>
Do you want Mary's update to fail because of a concurrency conflict? When
it
fails, how do you want to deal with the conflict?
>
Your current code appears to read the updated record and then apply the
old
values to it. This gets rid of the concurrency conflict but you still end
up
with your old salary instead of your raise.
>
My choice would be to inform the user that the record has been changed by
another user and let the user reload the record and start over.
>
Kerry Moorman
>
"John" wrote:
>

>So Kerry how do I handle it? which was my original question.
>>
>Regards
>>
>>
>"Kerry Moorman" <KerryMoorman@d iscussions.micr osoft.comwrote in message
>news:31F1C26 5-0B1C-40DB-8174-3A5F6DA4DD8F@mi crosoft.com...

John,
>
It looks like your approach to concurrency handling is to get around
the
concurrency error by reloading the data from the database and then
applying
your changes.
>
You might as well just turn off concurrency checking, since that is the
end
result anyway.
>
In other words, it looks like your code is just avoiding concurrency
exceptions, not handling concurrency conflicts.
>
Kerry Moorman
>
"John" wrote:
>
>Hi
>>
>I have developed the following logic to handle db concurrency
>violations.
>I
>just wonder if someone can tell me if it is correct or if I need a
>different approach.Would love to know how pros handle it.
>>
>Thanks
>>
>Regards
>>
>>
> Dim dc As DataColumn
> Dim drCache As DataRow
> Dim drCurrent As DataRow
>>
> Try
> ' Attempt the update
> daContacts.Upda te(ds.Contacts)
>>
> Catch Ex As DBConcurrencyEx ception
>>
> ' First - cache the row
> drCache = ds.Contacts.New Row()
> For Each dc In ds.Contacts.Col umns
> If Not dc.ReadOnly Then
> drCache(dc.Colu mnName) = Ex.Row(dc.Colum nName)
> End If
> Next
>>
> ' Refresh from database
> daContacts.Fill (ds.Contacts)
>>
> ' Position to the faulted row
> drCurrent = ds.Contacts.Row s.Find(Ex.Row(" ID"))
>>
> ' Apply User Changes
> For Each dc In ds.Contacts.Col umns
> If Not dc.ReadOnly Then
> drCurrent(dc.Co lumnName) = drCache(dc.Colu mnName)
> End If
> Next
>>
> ' Save again
> daContacts.Upda te(ds.Contacts)
> End Try
>>
>>
>>

>>
>>
>>

**=?Utf-8?B?S2VycnkgTW9vcm1hbg==?=** · Mar 27 '08, 06:45 PM

Re: Handling concurrency violations

John,

I don't display both new and old values to the user, so I don't have any
code examples.

However, this book has a section on just that topic. I can highly recommend
this book in general:

Programming Microsoft ADO.NET 2.0 Core Reference by David Sceppa

Kerry Moorman

"John" wrote:

Hi Kerry
>
Many thanks for this insight. Is there an easy way to display both new and
old row values to the user to let him/her select?
>
Thanks
>
Regards
>
"Kerry Moorman" <KerryMoorman@d iscussions.micr osoft.comwrote in message
news:287D48C5-72D5-4A42-A59F-211AF9599F66@mi crosoft.com...

John,

You need to decide how you want to handle concurrency issues in a
particular
application.

For example, how do you want to handle this situation:

Mary loads your employee record from the Employees table into the Employee
Manager application. She loaded your record because your cell phone number
has changed and she is updating that piece of information in your record.

While Mary is working on your record, Jim loads your employee record from
the Employees table into the Employee Manager application. He loaded your
record because you have just gotten a big raise and he is updating that
piece
of information in your record. He changes your salary and updates your
record
in the database.

Mary has now finished changing your cell phone number and attempts to
update
your record in the database.

Do you want Mary's update to succeed? If it does you have just lost your
raise because her update will overwrite your new salary that Jim entered
with
your old salary as it was when Mary loaded your record.

Do you want Mary's update to fail because of a concurrency conflict? When
it
fails, how do you want to deal with the conflict?

Your current code appears to read the updated record and then apply the
old
values to it. This gets rid of the concurrency conflict but you still end
up
with your old salary instead of your raise.

My choice would be to inform the user that the record has been changed by
another user and let the user reload the record and start over.

Kerry Moorman

"John" wrote:

So Kerry how do I handle it? which was my original question.
>
Regards
>
>
"Kerry Moorman" <KerryMoorman@d iscussions.micr osoft.comwrote in message
news:31F1C265-0B1C-40DB-8174-3A5F6DA4DD8F@mi crosoft.com...
John,

It looks like your approach to concurrency handling is to get around
the
concurrency error by reloading the data from the database and then
applying
your changes.

You might as well just turn off concurrency checking, since that is the
end
result anyway.

In other words, it looks like your code is just avoiding concurrency
exceptions, not handling concurrency conflicts.

Kerry Moorman

"John" wrote:

Hi
>
I have developed the following logic to handle db concurrency
violations.
I
just wonder if someone can tell me if it is correct or if I need a
different approach.Would love to know how pros handle it.
>
Thanks
>
Regards
>
>
Dim dc As DataColumn
Dim drCache As DataRow
Dim drCurrent As DataRow
>
Try
' Attempt the update
daContacts.Upda te(ds.Contacts)
>
Catch Ex As DBConcurrencyEx ception
>
' First - cache the row
drCache = ds.Contacts.New Row()
For Each dc In ds.Contacts.Col umns
If Not dc.ReadOnly Then
drCache(dc.Colu mnName) = Ex.Row(dc.Colum nName)
End If
Next
>
' Refresh from database
daContacts.Fill (ds.Contacts)
>
' Position to the faulted row
drCurrent = ds.Contacts.Row s.Find(Ex.Row(" ID"))
>
' Apply User Changes
For Each dc In ds.Contacts.Col umns
If Not dc.ReadOnly Then
drCurrent(dc.Co lumnName) = drCache(dc.Colu mnName)
End If
Next
>
' Save again
daContacts.Upda te(ds.Contacts)
End Try
>
>
>
>
>
>

>
>
>

Handling concurrency violations

Handling concurrency violations

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